For battery-powered radio apparatus, such as hand-held "walkie-talkie" transmitters and receivers, and relatively smaller-sized paging receivers intended to be carried on the clothing of a user, there are now available both rechargeable and non-rechargeable batteries or electric energy cells in similar sizes and configurations, giving a user the choice which type of battery to use in a given apparatus. To provide the user with added convenience, housings, of such apparatus have been fitted with exterior contacts for mating with a battery charger, and within the battery compartment of the housing these contacts are coupled to a battery when the latter is installed therein, so that the battery can be recharged without removing it from the battery compartment of the apparatus. In apparatus which can accept and use either type of battery in the same battery compartment, this is not an unmixed blessing. The possibility that a user who has installed a non-rechargeable battery might inadvertently couple the apparatus to a battery charger presents a real danger in that the attempt to recharge a mercury battery, for example, could cause the battery to explode. Care must also be exercised to avoid attempting to charge a rechargeable battery in the reverse-polarity direction. In the case of a nickel-cadmium (Ni Cad) battery, reverse charging can irretrievably ruin the battery.